docs: def T(self) -> "Histogram2D":
          """Histogram with swapped axes.
  
          Returns
          -------
          Histogram2D - a copy with swapped axes
          """
          a_copy = self.copy()
          a_copy._binnings = list(reversed(a_copy._binnings))
          a_copy.axis_names = list(reversed(a_copy.axis_names))
          a_copy._frequencies = a_copy._frequencies.T
          a_copy._errors2 = a_copy._errors2.T
          return a_copy